Exactly the same configuration in all the tab of administration, between my VPS with Ubuntu 12.04, 1 CPU cores, 2.000 MHz CPU-power, 1.024 MB RAM guaranteed - and my notebook, with Debian 6.0 Squeeze, Intel Duo Core @2.00 GHz, 4 GB Ram (3 GB free), with same PHP version and ./configure; the first run, the second doing this 503 error.

Exactly same happened to my personal computer, also with Debian 6.0.

Problem is not related with this version of PHP. Also with pre-bundled version of PHP, PHP 4.4.9 (litespeed) (built: Apr 12 2011 09:59:27)
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Zend Engine v1.3.0, Copyright (c) 1998-2004 Zend Technologies
problem is the same.